package org.apache.lucene.search;


import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;

import java.io.IOException;

/**
 * Implements the fuzzy search query. The similiarity measurement
 * is based on the Levenshtein (edit distance) algorithm.
 */
public final class FuzzyQuery extends MultiTermQuery {

  public final static float defaultMinSimilarity = 0.5f;
  private float minimumSimilarity;
  private int prefixLength;

  /**
   * Create a new FuzzyQuery that will match terms with a similarity
   * of at least <code>minimumSimilarity</code> to <code>term</code>.
   * If a <code>prefixLength</code> &gt; 0 is specified, a common prefix
   * of that length is also required.
   *
   * @param term              the term to search for
   * @param minimumSimilarity a value between 0 and 1 to set the required similarity
   *                          between the query term and the matching terms. For example, for a
   *                          <code>minimumSimilarity</code> of <code>0.5</code> a term of the same length
   *                          as the query term is considered similar to the query term if the edit distance
   *                          between both terms is less than <code>length(term)*0.5</code>
   * @param prefixLength      length of common (non-fuzzy) prefix
   * @throws IllegalArgumentException if minimumSimilarity is &gt; 1 or &lt; 0
   *                                  or if prefixLength &lt; 0 or &gt; <code>term.text().length()</code>.
   */
  public FuzzyQuery(Term term, float minimumSimilarity, int prefixLength) throws IllegalArgumentException {
    super(term);

    if (minimumSimilarity > 1.0f)
      throw new IllegalArgumentException("minimumSimilarity > 1");
    else if (minimumSimilarity < 0.0f)
      throw new IllegalArgumentException("minimumSimilarity < 0");
    this.minimumSimilarity = minimumSimilarity;

    if (prefixLength < 0)
      throw new IllegalArgumentException("prefixLength < 0");
    else if (prefixLength >= term.text().length())
      throw new IllegalArgumentException("prefixLength >= term.text().length()");
    this.prefixLength = prefixLength;
  }

  /**
   * Calls {@link #FuzzyQuery(Term, float) FuzzyQuery(term, minimumSimilarity, 0)}.
   */
  public FuzzyQuery(Term term, float minimumSimilarity) throws IllegalArgumentException {
    this(term, minimumSimilarity, 0);
  }

  /**
   * Calls {@link #FuzzyQuery(Term, float) FuzzyQuery(term, 0.5f, 0)}.
   */
  public FuzzyQuery(Term term) {
    this(term, defaultMinSimilarity, 0);
  }

  /**
   * Returns the minimum similarity that is required for this query to match.
   *
   * @return float value between 0.0 and 1.0
   */
  public float getMinSimilarity() {
    return minimumSimilarity;
  }

  /**
   * Returns the prefix length, i.e. the number of characters at the start
   * of a term that must be identical (not fuzzy) to the query term if the query
   * is to match that term.
   */
  public int getPrefixLength() {
    return prefixLength;
  }

  protected FilteredTermEnum getEnum(IndexReader reader) throws IOException {
    return new FuzzyTermEnum(reader, getTerm(), minimumSimilarity, prefixLength);
  }

  public String toString(String field) {
    return super.toString(field) + '~' + Float.toString(minimumSimilarity);
  }
}
